1. Field of the Invention
The present invention is in the field of navigation of vehicles. More specifically, the present invention relates to a method and apparatus for steering vehicles by using a steering control algorithm that takes into account the difference between the nominal and optimum positions of a navigation antenna.
2. Discussion of the Prior Art
The prior art GPS systems are used to manually or automatically steer a vehicle (like a tractor) along a predetermined path. To achieve an automatic steering, the GPS information is fed to a steering control algorithm which calculates an appropriate steering action to steer the tractor (or another vehicle) onto the prescribed trajectory and keep it on that trajectory.
However, the prior art automatic steering control algorithm is based, among other things, on the assumption that a GPS (or other navigation) antenna is mounted at a specific nominal location on the vehicle (like a tractor) at a predetermined reference point relative to its geometry, for example, on the top of the driver's cabin, or over the center of the rear axle.
The performance of the prior art automatic steering control algorithm is dependent on the accuracy of this nominal navigation antenna position. Moving the navigation antenna to a different location on the vehicle would result in the performance degradation of the automatic steering control algorithm, in the undesired weaving, or even in instability.
On the other hand, the variety of factors may prevent mounting the navigation antenna at the prescribed nominal location of the vehicle. For example, the prescribed nominal location in terms of the steering control algorithm for the GPS antenna (for example, the top of the driver's cabin, or the center of the rear axle) may be occupied by some other fixtures, such as a CB antenna, a projector, etc.
Thus, in many prior art cases, the actual navigation antenna location on the vehicle may be different from the nominal assumed navigation antenna location on the vehicle, which can significantly degrade the performance of the prior art automatic steering control algorithm.